The present invention generally relates to breast tumor screening devices and methods and, more particularly, is concerned with an in situ tumor temperature profile measuring probe and a method of using the probe.
The early detection of tumors, which is the principal strategy for reducing the mortality of breast cancer, is a challenging task. X-ray mammograms, widely used for mass screening, cannot reliably detect early tumors much below 1 cm in size. The false negative rate is 5 to 15% for tumors of palpable size. Mammography is inconclusive in differentiating malignant tumors from nonmalignant breast disease, such as harmless cysts and benign fibroid tissue. Ultrasound, which is commonly used to discriminate between tumor masses and cysts after indications are found with mammography, does not have the sensitivity to detect very small invasive tumors. Magnetic resonance (MR) imaging lacks sensitivity and specificity. With MR dynamic contrast methods, sensitivity is high but the specificity is not high enough to reliably resolve benign from cancerous lesions. Histo-pathological findings from biopsies are the only reliable means of breast cancer diagnosis and, consequently, many women are subjected to biopsies to improve their chances for long-term survival if any abnormality is found.
Angiogenesis is the growth of new blood vessels from existing capillaries. It is a fundamental process of tumor growth and metastasis. All solid tumors require angiogenesis for growth. This process has received much attention since it was first postulated in 1971. In breast cancer, it has been shown that the level of angiogenesis as defined by microvessel density has prognostic value. Studies have shown that the levels of angiogenesis in breast cancer are correlated with the potential for metastasis and aggressive growth. The angiogenic switch occurs early in tumor growth. A method that is sensitive to increased blood perfusion in a suspected lesion would be of value for early detection of breast cancer.
Tumors have a higher temperature than surrounding tissue by virtue of increased blood circulation in the tumor, particularly in the peripheral region of the tumor. Increased perfusion of arterial blood could set up a temperature gradient from the tumor interior to the surrounding tissue. It is believed that excess tumor temperature could also arise from the higher metabolic rates of growing tumor cells. This temperature excess has been visualized by surface thermography in the case of large tumors near the surface of the breast, though surface infrared thermography in clinical practice became controversial for a number of technical reasons.
It appears that no reliable or accepted data are available on the characteristics of tumor temperatures by other imaging methods or by in situ methods. In the former case, magnetic resonance (MR) imaging cannot produce an ab initio temperature map of tissue due to the variations of phase or frequency caused by variations in susceptibility of tissue. In the latter case, single-point temperature measurements are subject to considerable error due to heat conduction effects of the sensor itself and of unknown temperature gradients in the tissue. In situ probes for internal temperature must satisfy rigorous requirements on conduction of heat and thermal mass and must be capable of sensing small temperature gradients reliably. Tumor temperatures can only be inferred from non-invasive surface thermography images and, thus, are limited in sensitivity, resolution and accuracy.
Because current imaging modalities cannot completely identify all cancerous lesions, many biopsy procedures are performed. Surgical biopsy procedures are particularly expensive and uncomfortable to patients. The lesion is visualized and a localizing guide wire is placed through a small needle into the lesion. The needle is removed. The guide wire is left in place. The patient is taken to surgery for the surgical biopsy procedure in which the wire localizes the lesion center for the surgeons. A reduction of such procedures would be desirable. Other common biopsy procedures for the breast involve less invasive needle methods with vacuum aspiration.
The inventors herein have recognized the desirability of having a temperature probe that could be used to provide added information to radiologists and which would be helpful in avoiding more severe forms of biopsy procedures. However, problems exist with current temperature probes which are found in the prior art. Current temperature probes are relatively large. The smallest conventional thermocouple wires are about 120 micrometers in diameter and are very fragile. Two such wires are needed for each probe element. The thermal conductivity of the wires in these relatively large probes affects the temperature measurements made by the probe with the result being that the probe does not measure tumor temperatures with high accuracy.
Consequently, a need remains for a tumor temperature probe which is smaller in size than prior art probes and can provide reliable and sensitive temperature measurements and thus would overcome the aforementioned problems of the prior art probes, without introducing any new problems in place thereof.